Certain colloid clays will swell in water to many times their dry volume and as such have utility as gelling or thickening agents for control of the rheological properties of a variety of materials. These naturally occurring clays are generally not compatible with a number of organic based compositions with regard to the control of rheological properties. Hence, it is necessary to organically modify these clays to make them compatible with organic materials, and such clays are generally referred to as "organophilic" clays or "organo-clays." These clays have a large number of uses for thickening organic compositions such as paints, lubricants, cable filling compositions and the like.
The basic starting material used to make organophilic clay is an exchangeable clay of the smectite group and can include montmorillonite, (commonly known and mined as bentonite), hectorite, saponite, attapulgite and sepiolite. These clays include exchangeable cationic species such as sodium, potassium or calcium ions on their species such as sodium, potassium or calcium ions on their surface. In the course of manufacturing an organophilic clay, at least a portion of these exchangeable cationic species are substituted by an organic cation such as a quaternary amine, an organophosphorus ion or the like. The addition of the organic group modifies the clay making it compatible with organic compositions and in general allowing it to provide rheological modification in select organic fluids.
There is a large body of prior art relating to the manufacture of organophilic clays. For example, U.S. Pat. Nos. 2,531,427 and 2,531,440 both disclose general processes for the manufacture of organically substituted clays. U.S. Pat. No. 5,110,501 discloses a later process for preparing an organophilic clay in which a slurry of clay is subjected to high shear in a Manton-Gaulin Homogenizer.
In general, clays are characterized by a complicated microstructure in which lamellar sheets of material are stacked, folded, or pleated into complex layered structures. Conventional wisdom has heretofore taught that in order to manufacture a high quality, organically substituted clay it is necessary to process the clay under very high shear conditions and in the form of a slurry or dispersion so as to open the lamellar structure and permit the ion exchange reaction to take place in the aqueous medium. In general, the final product of such reactions is sold and used in the form of a pulverized material; therefore, processing in a liquid or slurry state necessitates filtration, dewatering and drying steps. Clearly, it would be desirable to carry out processing on a material having a low water content. Previous attempts have been made to prepare organophilic clays by mixing non-slurried clays with the appropriate reagents; however, products produced by such prior art processes have low degrees of organic substitution and they delaminate poorly in use and they provide low quality performance.
There is a need for a method whereby organically substituted clays may be manufactured in a process which does not require the starting clay to be in the form of a dispersion or slurry. It is further desirable that any such process be amenable to operation on a continuous basis and that it be capable of producing high quality modified clay. The present invention, as will be explained in greater detail hereinbelow, provides a method whereby dry clay may be efficiently reacted with an organic cation to thereby render it organophilic. The processing equipment is simple in construction and readily amenable to continuous operation. The modified clay produced by the present invention is of very high quality; and most notably when it is incorporated in a hydrocarbon oil, it produces a thickened gel characterized by a dielectric constant which is temperature invariant over a large range. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.